PHILADELPHIA -- The 2013 season could not have started much better for left-hander Jesse Biddle. The Phillies' top prospect, as ranked by MLB.com, dazzled almost immediately for Double-A Reading, setting off speculation about when he might be ready to make his Major League debut.

Unfortunately for Biddle, 22, who has received an invitation to big league camp next month in Clearwater, Fla., the rest of the 2013 season did not go as well as that first month, and that highly anticipated debut is still on the horizon.

In his first Double-A season, Biddle wasted no time showcasing his dominance. In one April start, he threw seven innings of one-hit ball, striking out 16 in the process. In his next outing, Biddle allowed just one hit over six innings to go along with 10 strikeouts.

Things started to unravel a bit, however, as Biddle struggled with an illness that was later diagnosed as pertussis, better known as whooping cough. In addition, a postseason MRI revealed that he had pitched the final month of the season with plantar fasciitis in his left foot. It all led to a 5-14 record, despite a respectable 3.64 ERA, and a seemingly endless amount of frustration.

Still, Biddle feels that the entire experience will ultimately benefit him in the long run.

"It was huge for my growth, really. My maturity went through the roof," Biddle said. "I was really, really immature in some ways handling my illnesses, handling some of the adversity I was facing. There were a lot of times I failed last year, and I didn't handle it the right way. There are some things I really want to grow up on and want to improve, and that's why I'm here, that's why I'm working."

Though Phils director of player development Joe Jordan believes the illnesses "played a big part" in Biddle's performance last season, he said the young hurler worried "too much about too many things." Jordan told Biddle as much when the two met in October, and Biddle has already started to coach himself on how to better handle himself in the future.

"A big thing for me will just be not sitting on things as long," Biddle said. "There are times where I'll let a game affect me for too long after the game is over, when the fact is, once my manager takes the ball out of my hands, there's nothing I can do. As much as I want to, as much as I want to go back and replay it over and over in my head, there's nothing I can do to change it."

In addition to getting Biddle to worry less about matters that are out of his control, Jordan would like to see him develop more consistency with his control.

Though Biddle has increased his strikeout rate in each of the last three years, despite moving up a level each season, he has struggled at times with walks. He lowered his walk rate, from 4.5 per nine innings with Class A Lakewood in 2011 to just 3.4 per nine with Class A Advanced Clearwater in 2012. But that number spiked with Reading last season, however, as Biddle issued 82 walks in 138 1/3 innings.

"It's about consistency at this point; things like throwing your fastball on the side of the plate you're trying to when you want to," Jordan said. "That's what he needs to get to, because he's got the weapons to be a very, very good starter for us, we all know that."

As far as the walks are concerned, Jordan isn't worried about the potentially alarming rates at this point. After all, Jordan recalls drafting another pitcher during his days as a scout with the Expos who dealt with a similar issue at that age -- and things seemed to turn out pretty well for that southpaw.

Ironically enough, that fourth-round pick in 2000 is current Phillies ace Cliff Lee.

"When I was an area scout, I drafted a left-hander out of the University of Arkansas that was a junior, 21 years old -- about the same age as Jesse Biddle. He walked 53 guys in 65 innings [at Arkansas], almost one an inning. Same age. Jesse wasn't near that bad," Jordan said. "And that guy right now, for the Philadelphia Phillies, throws the ball right where he's trying to almost every time out about 30 out of 34 starts a year. You can't even imagine him walking one an inning anymore."

In fact, in 2010, Lee issued just 18 walks over 212 1/3 innings, which works out to less than one per nine innings. His ratio of 0.8 walks per nine innings led the Majors that season, and he again led the league in that category in both in 2012 and '13.

"At the same age, [Biddle] was better -- and it wasn't even close," Jordan said. "And Cliff will hate me for saying that."

What the future holds for Biddle -- including even where he will start the upcoming season after beginning spring camp with the Phils -- remains unknown. Showcasing his new mind-set, he isn't letting himself worry about where he'll begin the season, since the decision is entirely out of his control. Instead, Biddle simply has his sights set on making the most of his time in Clearwater.

"Like a sponge, I'm just going to take everything in and try to absorb it," Biddle said. "I'm going to ask a lot of questions -- hopefully not too many, but I'm going to ask questions, and I'm just going to learn. That's what it comes down to -- just trying to get better every day, whether it's on the field or off the field. You can't pitch every day, so you've got to learn something else on those days."

Paul Casella is a reporter for MLB.com. Follow him on Twitter @paul_casella. This story was not subject to the approval of Major League Baseball or its clubs.